1. Field of the Invention
This invention relates generally to a method and apparatus for controlling an internal combustion engine and more particularly to a microprocessor-based electronic engine control system having a memory preprogrammed with various control laws and control schedules responsive to one or more sensed engine-operating parameters and generating control signals for fuel injection, ignition timing, EGR control, and the like.
2. Statement of the Prior Art
Many of the patents of the prior art recognize the need for employing the enhanced accuracy of digital control systems for more accurately controlling one or more functions of an internal combustion engine.
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 3,904,856 which issued to Louis Monptit on Sept. 9, 1975 and U.S. Pat. No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. All of these Patents represent a break-away from the purely analog control systems of the past, but neither the accuracy, reliability, or number of functions controlled is sufficient to meet present day requirements.
Future internal combustion engines will require that emissions be tightly controlled while due to ever-increasing governmental regulations, while fuel consumption is minimized and drivability improved over the entire operating range of the engine. None of the systems of the prior art provide a method and apparatus for controlling the operation of an internal combustion engine with sufficient accuracy to attain minimal emissions and minimal fuel consumption together with improved drivability.
The systems of the prior art attempt to control one or more of the engine operating functions but none attempts to control the operation of the fuel pump, fuel injection, engine ignition timing on-off and/or proportional EGR control, and the like while using feedback from such devices as oxygen sensors for emission control purposes or for effecting a closed loop fuel control operations, and yet including provisions for optimizing acceleration enrichment handling, and the like. Moreover, the systems of the prior art are extremely expensive, difficult to repair and maintain and are, therefore, not commercially feasible at the present time.
These and other problems of the prior art are solved by the microprocessor-based electronic engine control system of the present invention which eliminates most or all of the problems of the prior arts and enables a commercially feasible implementation of a digital control system having a relatively low cost, and which is easy to repair and maintain. The system of the present invention is able to implement much more advanced and complex fuel control laws and expand the various control functions performed thereby to include ignition timing and on-off and/or proportional EGR control while, at the same time, reducing the cost and size of the unit and increasing reliability so as to render the system commercially feasible.
Another problem existing in the prior art is that electronically controlled fuel systems are subject to failure and a failure could conceivably occur in which a fuel injection pulse were left on so that fuel continued to be injected or supplied to the engine even after some catastrophic failure. The present invention also supplies means for automatic fuel shut-off upon the detection of a failure in the system.